: Habituation (i.e., decreases in responding) and sensitization (i.e., increases in responding) following prolonged or repeated exposures to a fixed stimulus, have been identified as important in adaptation to repeated or prolonged noxious stimulation. Determinants of habituation or sensitization are poorly understood, and experimental investigation of habituation of pain ratings have generally relied on pain reports and statistical techniques that average responses across a group of participants...

Although patients suffering from major depressive disorder (MDD) often complain from painful symptoms, the relationship between experimental pain processes and depression has yet to be clearly characterized. Only recently have studies employing temporal summation (TS) paradigms offered preliminary insight into the co-occurrence of pain and depression. This study sets out to evaluate the contribution of spinal and supraspinal processes in pain sensitization in MDD using a TS paradigm. Thirteen volunteers with no psychiatric disorders (controls) and fourteen MDD subjects were included in the analysis...

BACKGROUND: Menstrually-related headache and headaches associated with oestrogen withdrawal are common conditions, whose pathophysiology has not been completely elucidated. In this study we evaluated the influence of combined hormonal contraceptives (CHC) on pain threshold in women presenting migraine attacks during hormone-free interval. FINDINGS: Eleven women with migraine attacks recurring exclusively during the oestrogen-withdrawal period were studied with the nociceptive flexion reflex, a neurophysiological assessment of the pain control systems, during the third week of active treatment and during the hormone-free interval...

PURPOSE: Premenstrual dysphoric disorder (PMDD) is characterized by severe affective and physical symptoms, such as increased pain, during the late-luteal phase of the menstrual cycle. The mechanisms underlying hyperalgesia in women with PMDD have yet to be identified, and supraspinal pain modulation has yet to be examined in this population. The present study assessed endogenous pain inhibitory processing by examining conditioned pain modulation (CPM, a painful conditioning stimulus inhibiting pain evoked by a test stimulus at a distal body site) of pain and the nociceptive flexion reflex (NFR, a spinally-mediated withdrawal reflex) during the mid-follicular, ovulatory, and late-luteal phases of the menstrual cycle...

Flexion/withdrawal reflexes are attenuated by spinal, intracerebroventricular (ICV) and systemic delivery of cholinergic agonists. In contrast, some affective reactions to pain are suppressed by systemic cholinergic antagonism. Attention to aversive stimulation can be impaired, as is classical conditioning of fear and anxiety to aversive stimuli and psychological activation of stress reactions that exacerbate pain. Thus, in contrast to the suppressive effects of cholinergic agonism on reflexes, pain sensitivity and affective reactions to pain could be attenuated by reduced cerebral cholinergic activation...

Several observations suggest that respiratory phase (inhalation vs. exhalation) and post-inspiratory breath-holds could modulate pain and the nociceptive reflex. This experiment aimed to investigate the role of both mechanisms. Thirty-two healthy participants received supra-threshold electrocutaneous stimulations to elicit both the Nociceptive Flexion Reflex (NFR) and pain, either during spontaneous inhalations or exhalations, or during three types of instructed breath-holds: following exhalation, at mid-inhalation and at full-capacity inhalation...

OBJECTIVE: To reanalyze scoring criteria for automatic detection of nociceptive flexion reflexes (NFRs) in electromyography (EMG) recordings and to improve detection accuracy by accounting for multiple characteristics of the recordings, such as baseline noise level or sampling rate. METHODS: Single scoring criteria for the NFR were reanalyzed and validated against an independent data set. To account for influences on the single scoring criteria, such as the baseline noise, multivariate classification models were derived...

OBJECTIVE: to analyze the frequency of different forms of temporomandibular joint dysfunction (TMJD) in episodic and chronic migraine and to study mechanisms of their comorbidity. MATERIAL AND METHODS: Sixty-three patients with chronic migraine (CM) and 40 patients with episodic migraine (EM) were examined. Anxiety and depression were assessed with the HADS, quality-of-life related to headache was measured with the HIT-6. To evaluate the antinociceptive system function, we studied blink reflex (BR) and nociceptive flexion reflex (NFR)...

Research studies have begun to identify altered neurophysiological mechanisms that develop as a consequence of chronic painful knee arthritis. Neuroplastic changes may occur in nociceptive pathways, thereby contributing to heightened chronic pain and spread of symptoms, as well as diminished quality of life. One biomarker for examining central sensitization of nociceptive pathways is the measurement of flexion reflex excitability, also called the nociceptive reflex. In a recent article in Arthritis Research & Therapy, Rice and colleagues utilize this biomarker to analyze the clinical and neurophysiological effects of a very common and typical medical intervention, joint aspiration and intra-articular corticosteroid injection...

This study examines the effect of normal aging on temporal summation (TS) of pain and the nociceptive flexion reflex (RIII). Two groups of healthy volunteers, young and elderly, received transcutaneous electrical stimulation applied to the right sural nerve to assess pain and the nociceptive flexion reflex (RIII-reflex). Stimulus intensity was adjusted individually to 120% of RIII-reflex threshold, and shocks were delivered as a single stimulus or as a series of 5 stimuli to assess TS at 5 different frequencies (0...

Pain catastrophizing is associated with enhanced pain; however, the mechanisms by which it modulates pain are poorly understood. Evidence suggests that catastrophizing modulates supraspinal processing of pain but does not modulate spinal nociception (as assessed by nociceptive flexion reflex [NFR]). Unfortunately, most NFR studies have been correlational. To address this, this study experimentally reduced catastrophizing to determine whether it modulates spinal nociception (NFR). Healthy pain-free participants (N = 113) were randomly assigned to a brief 30-minute catastrophizing reduction manipulation or a control group that received pain education...

OBJECTIVE: To investigate how the nociceptive withdrawal reflex (NWR) is modulated during gait initiation. METHODS: The NWR was elicited in ten subjects using electrical stimulation at four sites in the right foot during symmetrical stance (50% of body weight on each foot) or while performing the first step during gait initiation: either during heel off (HO, 20% of body load on the starting leg) or heel contact (HC, 80% of body load on the starting leg in the first step)...

Temporal predictability, or knowing when a noxious stimulus will occur, has been implicated in stress-induced hypoalgesia, but the contribution of event predictability, or knowing what the stimulus will be, remains poorly understood. To address this issue, we examined the effects of event predictability on pain intensity ratings and nociceptive flexion reflex responses. Participants repeatedly experienced five intensities of electrocutaneous stimulation, ranging from nonpainful to extremely painful, delivered either randomly (unpredictability group) or blocked (predictability group) with no cues provided...

OBJECTIVE: To investigate changes in clinical (physical and psychological) features of individuals with chronic whiplash-associated disorder who had previously undergone cervical radiofrequency neurotomy at the time point when the effects of radiofrequency neurotomy had dissipated and pain returned. DESIGN: Prospective cohort observational trial of consecutive patients. SETTING: Tertiary spinal intervention centre in Calgary, Alberta, Canada...

The nociceptive flexion reflex (NFR) is a widely used tool to investigate spinal nociception for scientific and diagnostic purposes, but its clinical use is currently limited due to the painful measurement procedure, especially restricting its applicability for patients suffering from chronic pain disorders. Here we introduce a less painful algorithm to assess the NFR threshold. Application of this new algorithm leads to a reduction of subjective pain ratings by over 30% compared to the standard algorithm. We show that the reflex threshold estimates resulting from application of the new algorithm can be used interchangeably with those of the standard algorithm after adjusting for the constant difference between the algorithms...

Testing of reflexes such as flexion/withdrawal or licking/guarding is well established as the standard for evaluating nociceptive sensitivity and its modulation in preclinical investigations of laboratory animals. Concerns about this approach have been dismissed for practical reasons - reflex testing requires no training of the animals; it is simple to instrument; and responses are characterized by observers as latencies or thresholds for evocation. In order to evaluate this method, the present review summarizes a series of experiments in which reflex and operant escape responding are compared in normal animals and following surgical models of neuropathic pain or pharmacological intervention for pain...

OBJECTIVE: Sex differences in pain are well established, with women reporting greater incidence of clinical pain and heightened responsivity to experimental pain stimuli relative to men. Sex hormones (ie, estrogens, progestins, androgens) could contribute to extant differences in pain sensitivity between men and women. Despite this, there has been limited experimental research assessing the relationship between pain and sex hormones. The purpose of this study was to extend previous research and examine the association between sex hormones and nociceptive processing in healthy women...